blob: 24d4e3783113d6ca251193d87170c4e9dde6462f [file] [log] [blame]
/*
* Copyright (c) 2016 Wind River Systems, Inc.
*
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @file @brief mutex kernel services
*
* This module contains routines for handling mutex locking and unlocking.
*
* Mutexes implement a priority inheritance algorithm that boosts the priority
* level of the owning thread to match the priority level of the highest
* priority thread waiting on the mutex.
*
* Each mutex that contributes to priority inheritance must be released in the
* reverse order in which it was acquired. Furthermore each subsequent mutex
* that contributes to raising the owning thread's priority level must be
* acquired at a point after the most recent "bumping" of the priority level.
*
* For example, if thread A has two mutexes contributing to the raising of its
* priority level, the second mutex M2 must be acquired by thread A after
* thread A's priority level was bumped due to owning the first mutex M1.
* When releasing the mutex, thread A must release M2 before it releases M1.
* Failure to follow this nested model may result in threads running at
* unexpected priority levels (too high, or too low).
*/
#include <zephyr/kernel.h>
#include <zephyr/kernel_structs.h>
#include <zephyr/toolchain.h>
#include <ksched.h>
#include <zephyr/wait_q.h>
#include <errno.h>
#include <zephyr/init.h>
#include <zephyr/syscall_handler.h>
#include <zephyr/tracing/tracing.h>
#include <zephyr/sys/check.h>
#include <zephyr/logging/log.h>
LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
/* We use a global spinlock here because some of the synchronization
* is protecting things like owner thread priorities which aren't
* "part of" a single k_mutex. Should move those bits of the API
* under the scheduler lock so we can break this up.
*/
static struct k_spinlock lock;
int z_impl_k_mutex_init(struct k_mutex *mutex)
{
mutex->owner = NULL;
mutex->lock_count = 0U;
z_waitq_init(&mutex->wait_q);
z_object_init(mutex);
SYS_PORT_TRACING_OBJ_INIT(k_mutex, mutex, 0);
return 0;
}
#ifdef CONFIG_USERSPACE
static inline int z_vrfy_k_mutex_init(struct k_mutex *mutex)
{
Z_OOPS(Z_SYSCALL_OBJ_INIT(mutex, K_OBJ_MUTEX));
return z_impl_k_mutex_init(mutex);
}
#include <syscalls/k_mutex_init_mrsh.c>
#endif
static int32_t new_prio_for_inheritance(int32_t target, int32_t limit)
{
int new_prio = z_is_prio_higher(target, limit) ? target : limit;
new_prio = z_get_new_prio_with_ceiling(new_prio);
return new_prio;
}
static bool adjust_owner_prio(struct k_mutex *mutex, int32_t new_prio)
{
if (mutex->owner->base.prio != new_prio) {
LOG_DBG("%p (ready (y/n): %c) prio changed to %d (was %d)",
mutex->owner, z_is_thread_ready(mutex->owner) ?
'y' : 'n',
new_prio, mutex->owner->base.prio);
return z_set_prio(mutex->owner, new_prio);
}
return false;
}
int z_impl_k_mutex_lock(struct k_mutex *mutex, k_timeout_t timeout)
{
int new_prio;
k_spinlock_key_t key;
bool resched = false;
__ASSERT(!arch_is_in_isr(), "mutexes cannot be used inside ISRs");
SYS_PORT_TRACING_OBJ_FUNC_ENTER(k_mutex, lock, mutex, timeout);
key = k_spin_lock(&lock);
if (likely((mutex->lock_count == 0U) || (mutex->owner == _current))) {
mutex->owner_orig_prio = (mutex->lock_count == 0U) ?
_current->base.prio :
mutex->owner_orig_prio;
mutex->lock_count++;
mutex->owner = _current;
LOG_DBG("%p took mutex %p, count: %d, orig prio: %d",
_current, mutex, mutex->lock_count,
mutex->owner_orig_prio);
k_spin_unlock(&lock, key);
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, lock, mutex, timeout, 0);
return 0;
}
if (unlikely(K_TIMEOUT_EQ(timeout, K_NO_WAIT))) {
k_spin_unlock(&lock, key);
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, lock, mutex, timeout, -EBUSY);
return -EBUSY;
}
SYS_PORT_TRACING_OBJ_FUNC_BLOCKING(k_mutex, lock, mutex, timeout);
new_prio = new_prio_for_inheritance(_current->base.prio,
mutex->owner->base.prio);
LOG_DBG("adjusting prio up on mutex %p", mutex);
if (z_is_prio_higher(new_prio, mutex->owner->base.prio)) {
resched = adjust_owner_prio(mutex, new_prio);
}
int got_mutex = z_pend_curr(&lock, key, &mutex->wait_q, timeout);
LOG_DBG("on mutex %p got_mutex value: %d", mutex, got_mutex);
LOG_DBG("%p got mutex %p (y/n): %c", _current, mutex,
got_mutex ? 'y' : 'n');
if (got_mutex == 0) {
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, lock, mutex, timeout, 0);
return 0;
}
/* timed out */
LOG_DBG("%p timeout on mutex %p", _current, mutex);
key = k_spin_lock(&lock);
struct k_thread *waiter = z_waitq_head(&mutex->wait_q);
new_prio = (waiter != NULL) ?
new_prio_for_inheritance(waiter->base.prio, mutex->owner_orig_prio) :
mutex->owner_orig_prio;
LOG_DBG("adjusting prio down on mutex %p", mutex);
resched = adjust_owner_prio(mutex, new_prio) || resched;
if (resched) {
z_reschedule(&lock, key);
} else {
k_spin_unlock(&lock, key);
}
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, lock, mutex, timeout, -EAGAIN);
return -EAGAIN;
}
#ifdef CONFIG_USERSPACE
static inline int z_vrfy_k_mutex_lock(struct k_mutex *mutex,
k_timeout_t timeout)
{
Z_OOPS(Z_SYSCALL_OBJ(mutex, K_OBJ_MUTEX));
return z_impl_k_mutex_lock(mutex, timeout);
}
#include <syscalls/k_mutex_lock_mrsh.c>
#endif
int z_impl_k_mutex_unlock(struct k_mutex *mutex)
{
struct k_thread *new_owner;
__ASSERT(!arch_is_in_isr(), "mutexes cannot be used inside ISRs");
SYS_PORT_TRACING_OBJ_FUNC_ENTER(k_mutex, unlock, mutex);
CHECKIF(mutex->owner == NULL) {
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, unlock, mutex, -EINVAL);
return -EINVAL;
}
/*
* The current thread does not own the mutex.
*/
CHECKIF(mutex->owner != _current) {
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, unlock, mutex, -EPERM);
return -EPERM;
}
/*
* Attempt to unlock a mutex which is unlocked. mutex->lock_count
* cannot be zero if the current thread is equal to mutex->owner,
* therefore no underflow check is required. Use assert to catch
* undefined behavior.
*/
__ASSERT_NO_MSG(mutex->lock_count > 0U);
LOG_DBG("mutex %p lock_count: %d", mutex, mutex->lock_count);
/*
* If we are the owner and count is greater than 1, then decrement
* the count and return and keep current thread as the owner.
*/
if (mutex->lock_count > 1U) {
mutex->lock_count--;
goto k_mutex_unlock_return;
}
k_spinlock_key_t key = k_spin_lock(&lock);
adjust_owner_prio(mutex, mutex->owner_orig_prio);
/* Get the new owner, if any */
new_owner = z_unpend_first_thread(&mutex->wait_q);
mutex->owner = new_owner;
LOG_DBG("new owner of mutex %p: %p (prio: %d)",
mutex, new_owner, new_owner ? new_owner->base.prio : -1000);
if (new_owner != NULL) {
/*
* new owner is already of higher or equal prio than first
* waiter since the wait queue is priority-based: no need to
* adjust its priority
*/
mutex->owner_orig_prio = new_owner->base.prio;
arch_thread_return_value_set(new_owner, 0);
z_ready_thread(new_owner);
z_reschedule(&lock, key);
} else {
mutex->lock_count = 0U;
k_spin_unlock(&lock, key);
}
k_mutex_unlock_return:
SYS_PORT_TRACING_OBJ_FUNC_EXIT(k_mutex, unlock, mutex, 0);
return 0;
}
#ifdef CONFIG_USERSPACE
static inline int z_vrfy_k_mutex_unlock(struct k_mutex *mutex)
{
Z_OOPS(Z_SYSCALL_OBJ(mutex, K_OBJ_MUTEX));
return z_impl_k_mutex_unlock(mutex);
}
#include <syscalls/k_mutex_unlock_mrsh.c>
#endif